The present invention relates to antenna pedestals and particularly to satellite tracking antenna pedestals used on ships and other mobile applications.
The invention is especially suitable for use aboard ship wherein an antenna is operated to track a transmitting station, such as a communications satellite, notwithstanding roll, pitch, yaw, and turn motions of a ship at sea.
Antennas used in shipboard satellite communication terminals typically are highly directive. For such antennas to operate effectively they must be pointed continuously and accurately in the direction toward the satellite.
When a ship changes its geographical position, or when the satellite changes its position in orbit, and when the ship rolls, pitches, yaws and turns, an antenna mounted on the ship will tend to become mis-pointed. In addition to these pointing disturbances the antenna will be subjected to other environmental stresses such as vibrations caused by shipboard machinery and shocks caused by wave pounding. All of these effects must be compensated for so that accurate antenna pointing can be maintained. Various stabilizing and motion-compensating antenna pedestals have been described in prior art (see U.S. Pat. Nos. 3,999,184, 3,358,285, 4,582,291, 3,893,123 and 3,860,931), however all of them suffer from one or more of the following disadvantages or deficiencies:
Limited ship motion accommodation PA0 Inadequate vibration and shock tolerance PA0 Poor pointing accuracy PA0 Excessive size and weight PA0 High cost PA0 Poor reliability PA0 Difficult maintenance
Compactness in size and lightness in weight are of paramount importance for antenna pedestals used on ships. Small ships and boats which operate in rough seas routinely experience roll amplitudes of .+-.35 degrees or more, pitch amplitudes of .+-.15 degrees, and repetitive wave pounding shocks of 2 g's. Antenna pedestals which are compact, and light yet rugged, which accommodate such effects and which avoid all of the above-listed disadvantages or deficiencies have not previously been available. Accordingly, it is a principle object of the present invention to provide an improved antenna pedestal apparatus wherein the foregoing deficiencies or disadvantages are substantially eliminated.
It is a primary object of the present invention to provide an improved stabilized antenna pedestal which occupies a minimum of space while accommodating very large amplitude ship motions.
It is a further object of the present invention to provide an improved shipboard antenna pedestal for use in a system for accurately tracking a satellite from ships in spite of elastic structural distortions (hull flexure) caused by rough seas.
It is a still further object of the present invention to provide an improved maritime satellite tracking antenna pedestal apparatus which provides accurate pointing, is reliable in operation, is easily maintained, uncomplicated, and economical to fabricate.
It is a still further object of the present invention to provide an improved stabilized antenna pedestal which is capable of rotational or tilting motions about a plurality of axes without requiting application of high driving torques.
It is a still further object of the present invention to provide an improved stabilized antenna pedestal which is substantially rigid and strong so as to be capable of withstanding moments, pressures, vibration, shock, and other forces when disposed in operational relationship with a ship at sea, as on the mast of the ship, and yet is light in weight.